Police are treating the death of father of three John Robert Day as suspicious.

His body was discovered by a passing motorist at 7.15am on Saturday at the base of the cutting on the northbound F6.

Yesterday, devastated family and friends gathered at the house of Mr Day's father in Farmborough Heights, some travelling from as far as Kempsey.

Known throughout the Farmborough Heights community as "Johnny", friends described Mr Day as a "gentle giant" devoted to his three young kids.

All were at a loss to explain Mr Day's death; theories included that he was hit by a car or was bashed and thrown from a cliff.

Detective Inspector Sean Gersbach, crime manager with Lake Illawarra Area Command, said police had appealed for five young men, occupants of a white VN Commodore seen in the area at the same time to come forward to help them with their enquiries.

The late 1980s model Commodore had distinctive dark stripes, possibly blue, along each side.

Insp Gersbach said "a variety of scenarios are possible", but police had not ruled out the scenario Mr Day had been chased.

"We are hoping there are not many VN Commodores out there that look like this," he said.

"We are hoping someone will have some knowledge of the owner or occupants of the vehicle.

"They may be completely innocent, but we just want to speak to them."

Police said Mr Day was last seen in the vicinity of Doyle Ave in Unanderra Industrial Park at 4.15am.

He was walking along Sylvester Ave and made an unusual right turn into the Doyle Ave cul-de-sac.

For some reason Mr Day, a man who police said knew the area well, had made his way up the hill of a vacant industrial lot towards the top of the F6 cuttings.

Police identified a single track at the top of the cutting where Mr Day had entered bushes at the top of the hill, broken through scrub and lantana for a distance of 5m before falling 20m to his death.

Police said they were aware of Mr Day's movements from 5pm on Friday night.

"We don't know what has happened between 4.15am and 7.15am," Mr Gersbach said.

Mr Day's body was found lying in the gutter between the cliff face and fence with an significant injury to the left side of his head.

Strikeforce Mulheran has been formed to investigate the death.

A post-mortem is expected to be carried out today and a report will be prepared by police for the coroner.

Investigators are urging anyone with information about the man's death or the VN Commodore sedan with the stripes to contact Lake Illawarra detectives on 4295 2699 or Crime Stoppers on 1800 333 000.